In commonly owned patent application Ser. No. 07/749,164 of J. Humpert (now U.S. Pat. No. 5,213,377) a fitting is described which is formed with an outwardly open generally cylindrical bore centered on an axis and having an inner surface of a predetermined inner diameter. A tube end fits axially into the bore and is formed with a radially outwardly open groove, and a partial stiff sleeve of elastically deformable and strong material is engaged in the groove and has a frustoconically outwardly flared sharp outer edge of a predetermined outer diameter. Interengaging formations on the sleeve and on the tube end spread the sleeve and force the edge to bite into the inner surface of the bore on axial outward displacement of the sleeve and tube end. An elastomeric seal ring on the tube end offset from the groove radially outwardly engages the bore. Such an arrangement constitutes a coupling that is extremely easy to put together, but virtually impossible to take apart.
In another known system described in German patent document 2,304,658 of W. L. Jones (claiming a British priority of Feb. 2, 1972) the tube end is provided with an O-ring and is formed at a short spacing outward of this seal with an outwardly projecting ridge that lies against the mouth of the bore when the tube end is fitted into the bore. A holddown plate formed with a hole that snugly surrounds the tube end is screwed down to the fitting to press the ridge against its outer face, thereby holding the tube end in place. This system is once again fairly complex in that it has several different parts even though it has the advantage of being susceptible of disassembly if required. It is also somewhat bulky so that it cannot readily be adapted to single-hole mounting faucets and the like.
German patent document 3,933,589 of G. Wachter et al describes a stab-type fast-action coupling where elastic tabs on the male part snap into place behind a radially inwardly projecting ridge of the female part to hold the two parts together. Thus assembly is very simple and the device is fairly compact. Nonetheless taking the joint apart is either impossible or requires a complex special-duty tool.